Diagnose and troubleshoot Azure Cosmos DB for NoSQL request time out exceptions

  • 05/09/2025
  • Applies to: ✅ NoSQL

Azure Cosmos DB for NoSQL returned an HTTP 408 request time out.

Troubleshooting steps

The following list contains known causes and solutions for request time out exceptions.

Check the service level agreement (SLA)

Check Azure Cosmos DB for NoSQL monitoring to see if the number of 408 exceptions violates the Azure Cosmos DB for NoSQL SLA.

Solution 1: It didn't violate the Azure Cosmos DB for NoSQL SLA

The application should handle this scenario and retry on these transient failures.

Solution 2: It did violate the Azure Cosmos DB for NoSQL SLA

Contact Azure Support.

Hot partition key

Azure Cosmos DB for NoSQL distributes the overall provisioned throughput evenly across physical partitions. When there's a hot partition, one or more logical partition keys on a physical partition are consuming all the physical partition's Request Units per second (RU/s). At the same time, the RU/s on other physical partitions are going unused. As a symptom, the total RU/s consumed are less than the overall provisioned RU/s at the database or container. You could still see throttling (429 errors) on the requests against the hot logical partition key. Use the Normalized RU Consumption metric to see if the workload is encountering a hot partition.

Solution

Choose a good partition key that evenly distributes request volume and storage. Learn how to change your partition key.

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